Can I render faster in cycles with a Radeon R5 graphics card?
I have experience with an R5, although I'm on a really crappy laptop here.

In my experience, OpenCL support for Cycles isn't that good. Slow, limited(no support for HDR textures, volumetrics, SSS), and the architecture still is pretty crappy. My AMD A8 usually does just fine for all rendering tasks. Then again, I'm on a crappy 4GB RAM computer, so test your setup.

In short, there is support. It is not guaranteed to actually be of assistance. Get a Nvidia if possible.